Oh no! Automatic updates for Ubuntu 10.04 Desktop stop in April (updates for 10.04 Server continue for two more years). Desktop users need to consider whether they'll upgrade to Ubuntu 12.04 LTS, which will receive updates for both Desktop and Server through 2017. This handy chart diagrams the situation. You can directly upgrade 10.04 (and 11.10) to 12.04, as explained here. Canonical's policy is that you get at least 18 months of updates for both Desktop and Server, and -- starting with 12.04 LTS -- 5 years of support for both desktop and server for LTS (Long Term Support) editions.

I've been an Ubuntu user since 2006, but I'm fed up with Unity and the other changes that Canonical makes to Ubuntu without user testing. So I'm going to Mint.

Mint 13 is based on Ubuntu 12.04, so it's supported until April 2017 (5 year support) for the Desktop as well as Server editions. Plus Mint 13 gives you a choice of Cinnamon, Mate, KDE, and Xfce interfaces.